1. Field of Invention
The invention relates to a combination lock having a means for defeating an automatic dialer. More specifically, the invention relates to such a combination lock wherein the defeating means comprises means for detecting the rotational speed of the spindle or shaft of the dial of the combination lock, and for blocking the combination lock when the speed of rotation exceeds a predetermined maximum.
2. Description of Prior Art
Combination locks are known in the art as illustrated in, for example, U.S. Pat. No. 4,142,388, Phillips et al, Mar. 6, 1979, U.S. Pat. No. 4,904,984, Gartner et al, Feb. 27, 1990 and U.S. Pat. No. 4,831,851, Larson, May 23, 1989. These are, of course, only some of the combination locks available in the art.
One of the problems which is faced by combination locks is that they can be defeated by automatic dialers. The automatic dialers comprise a computer controlled stepper motor which grasps the rotary dial of a combination lock and dials every possible combination of the combination lock at high speeds. With every possible combination being dialed, the correct combination for opening the lock will also be dialed. Accordingly, the lock can be opened without having knowledge of the combination.
Although this automatic dialer is very useful for legitimate owners of combination locks who have either lost or forgotten the combination, unfortunately, it can also be used by people wishing to make unlawful entry through a combination lock. With the high dialing speeds possible with the automatic dialer, the dialer can dial all possible combinations of even a combination lock having three tumbler wheels and a 100 number dial within twenty to thirty hours. Thus, a person wishing to make unlawful entry can place the automatic dialer on a combination lock in the late afternoon and return early next morning when there is a good chance that the lock will have been opened. Certainly, if the automatic dialer is left for a full weekend, the lock will definitely be opened before the end of the weekend.
In order for the automatic dialer to be useful, it must perform the dialing at high speeds. This means that the shaft or spindle of the dial of the combination lock must be rotated at a high speed.